Metal alkoxides are used for a wide variety of purposes. They are commonly employed catalysts in Ziegler polymerizations as well as in transesterification and condensation reactions. With partial or complete hydrolysis, alcoholysis or transesterification, they are used in coatings for plastics, textiles, glass and metals. Metal alkoxides are also used as additives for adhesives and paints and for the cross-linking or hardening of natural and synthetic materials.
Metal methoxides are also used for a wide variety of purposes. For example, tetramethyl titanate is used as a catalyst in the esterification of carboxylic acids with monohydric or polyhydric alkanols, particularly in the preparation of unsaturated esters which tend to polymerize in the presence of other esterification catalysts, thus reducing the yield of the monomeric ester. Tetramethyl titanate is also used as an ester interchange catalyst in the manufacture of higher esters from lower esters and as a catalyst in the manufacture of polyesters. Other metal methoxides can be used for similar purposes.
A commonly employed procedure for the production of metal alkoxides involves the reaction of a metal halide with an alcohol with the consequent generation of hydrogen halide. In order to progress to total alkoxylation of the metal, it is necessary that a hydrogen halide acceptor be present. Various patents disclosing the above reaction or variations on the above reaction are known.
The Nelles process, disclosed in U.S. Pat. No. 2,187,821, reacts a titanium tetrahalide with an alcohol in the presence of ammonia or an aliphatic or aromatic amine as a hydrogen halide acceptor. The reaction is also carried out in the presence of an inert organic solvent since the hydrogen halides formed are insoluble and easily separated.
A process for the conversion of titanium tetrahalides to titanate esters using amines and sulfonamides as catalysts is disclosed in U.S. Pat. No. 3,641,079. The reaction can be carried out in the liquid phase by using inert solvents.
U.S. Pat. No. 3,752,834 discloses the preparation of alkyl titanates by esterifying titanium tetrachloride with an alkanol, neutralizing the hydrochloric acid with ammonia and keeping the pH of the reaction mixture at about 4-6 until all the titanium tetrachloride has been introduced. Ammonia is then introduced until the pH of the reaction mixture is about 9.
U.S. Pat. No. 2,684,972 discloses a process for the production of inorganic esters wherein a metal halide is first reacted with ammonia and then the ammoniated compound is reacted with the appropriate alcohol. In the first step of the process disclosed in the above patent, the amount of ammonia added should be such that four atoms of nitrogen are combined with each titanium atom.
U.S. Pat. No. 2,654,770 discloses a method for the production of alkyl titanates wherein ammonia, a metal halide and an alcohol are admixed together to form an alkyl titanate and ammonium chloride. The ammonium chloride formed is then contained in a nitrogenous liquid selected from the group consisting of amides and nitriles.
U.S. Pat. No. 2,655,523 discloses a process for the formation of alkyl titanates wherein the ammonia used as the hydrogen chloride acceptor is present in slightly excess amounts.
U.S. Pat. No. 2,114,886 discloses a process for the purification of alkyl silicates wherein an alkyl silicate is treated with an amine to remove any residual hydrogen halide. The nitrogenous compound employed is soluble in the inorganic ester to be purified.
U.S. Pat. No. 3,268,566 discloses a process for the production of tetramethyl titanate wherein a tetraalkyl titanate is reacted with an alkanol.
U.S. Pat. No. 3,119,852 discloses a process for the formation of alkyl titanates wherein the alcohol is added to the titanium tetrachloride in a reverse addition mode. This patent also discloses the use of a solvent in which the ammonium chloride is insoluble.
U.S. Pat. No. 3,547,966 discloses a process for the production of trialkoxy monohalide titanium compounds. The reaction proceeds to the monohalide level (trialkoxy compound) when it is conducted at higher temperatures using a solvent whose boiling point is about the temperature at which the reaction is run.
French Patent of Addition, No. 92,060 reported at CA 71 91631, discloses the preparation of halogenated phenoxysilanes by reacting pentachlorophenol and trichlorosilane in the present of N,N'dimethylaniline.
While the processes detailed in the above patents are suited for the production of metal alkoxides derived from higher alcohols, i.e. C.sub.2 -C.sub.20 alkanols, they are not suitable for the production of metal alkoxides derived from lower alcohols, particularly methanol. These methoxides are often solids and it is difficult to separate them from the solid ammonium chloride formed. Separation problems also occur since ammonium chloride and solid metal methoxides exhibit similar solubility characteristics toward most commonly employed organic solvents. The alternative process for the production of a methoxide, such as tetramethyl titanate, involves either a transesterification or a trans alcoholysis exchange. While somewhat feasible alternatives, such processes are also expensive.